Ammonium polyphosphate (APP) is a kind of high-efficiency and environment-friendly flame retardants with high phosphor and nitrogen contents. It has different crystal types including crystal type I, II, III, IV, and V.
Among them, APP of crystal type II performs the best in thermal stability and water resistance so that it can be widely used in different fields, such as in plastic, fabric, leather, high-grade fire retardant coating, rubber paper, wood, fiber and so on. Its characteristics of low toxicity, none drippage and low smog make it be a good substitute for the halogen flame retardants.
At present, phosphorus pentoxide and diammonium hydrogen phosphate are used as raw materials to synthesize ammonium polyphosphate. The polymerization degree synthesized may be low resulting from various causes, such as the stoichiometric ratio of the reactants, the purity and activity of the reactants, incomplete ammonification reaction during the entire process, etc. Meanwhile, for the product, no protective treatment after discharging from the high temperature reactor kettle will lead to that the ammonium polyphosphate may have chain scission. Besides, the ammonium polyphosphate produced according to the conventional methods contains relatively more low molecular pre-polymer, and thus has worse water resistance and lower initial decomposition temperature.